Sucralose is a potent sweetener having sweetness several hundred times that of sucrose. It is chemically known as 1,6-dichloro-1,6-dideoxy-β-D-fructofuranosyl-4-chloro-4-deoxy-α-galactopyranoside and having formula is C12H19Cl3O8 and molecular weight 397.64. Sucralose is used as sweetner in beverage, as coating tablet, chewing gum and other food products. It is marketed by McNeil under tradename Splenda®.
It is also chemically known as 4,1′,6′-trichloro-4,1′,6′-trideoxygalactosucrose, (hereinafter referred to as “Sucralose”) involves the substitution of chlorine atoms in the sucrose molecule in one of the five secondary hydroxyl positions and in two of the three primary hydroxyl positions. This particular selection of positions usually means that any synthetic route must involve the preparation of an intermediate sucrose derivative having the required positions available for chlorination while the other positions are blocked. In particular, the reactive 6-position must not be chlorinated, while the 4-position must be rendered available for chlorination.
A process for preparing Sucralose is set forth in U.S. Pat. No. 4,362,869. This process converts sucrose through a number of steps into Sucralose. This process describes the sequential steps of (1) tritylation of sucrose to block the three primary alcohol groups; (2) acetylation of the five secondary alcohol groups as acetates; (3) detritylation of the three primary alcohol groups to deblock them; (4) acetyl migration from the 4-position to the 6-position; (5) chlorinating the desired alcohol groups at positions 4,1′, 6′; and (6) deblocking the remaining five alcohol groups by deacetylation thereby yielding Sucralose.
The schematic representation is as given below (Scheme I)

However, in this patent the purification of Sucralose is not mentioned.
U.S. Pat. No. 5,270,460 and WO2005090374 disclose the process of purification of Sucralose by silicagel chromatography or other chromatographic methods. However, purification of Sucralose by chromatographic method is commercially not feasible and cumbersome on large scale.
U.S. Pat. No. 4,801,700, U.S. Pat. No. 4,783,526, U.S. Pat. No. 5,141,860, U.S. Pat. No. 4,977,254 and GB2224504 disclose the process of purification of Sucralose by recrystallization from ethylacetate. This process provides Sucralose having some impurities which are difficult to remove even after repeated crystallization. Further, repeated crystallization would result in a loss of yield of the final product.
U.S. Pat. No. 4,380,476, U.S. Pat. No. 4,980,463 and U.S. Pat. No. 5,034,551 disclose the process of purification of Sucralose by crystallization from aqueous solution i.e. from water. However, there is substantial yield loss as Sucralose is highly soluble in water.
U.S. Pat. No. 5,498,709 and U.S. Application No. 20030171575 disclose the process of purification of Sucralose by crystallization from ethylacetate followed by recystallization from water. This process also requires repeated purification from different kind of solvents which may result in low yield.
U.S. Pat. No. 6,809,198 discloses the process of purification of Sucralose by cystallization from aqueous solution in controlled pH condition at pH 5.5 to 8.5 using buffer solution. This process requires regular monitoring of pH. It also requires special kind of industrial apparatus for the purification process. These drawbacks make the process cumbersome at an industrial scale.
U.S. Application No. 20030171574 discloses the process of purification of Sucralose by extractive method which involves repeated extraction from first solvent (i.e. water), second solvent (i.e. ethylacetate) and third solvent (i.e. ethylacetate).
This process also requires special kind of industrial apparatus to perform the purification. Moreover, this kind of process which requires repeated extraction is tedious and laborious to perform.
It is therefore, there is a need to develop a process for purification of Sucralose which not only overcomes the aforementioned problems but also provide a process which is simple, easy to handle and feasible at commercial production.
The final Sucralose is always contaminated with several unwanted polar impurities because of the nature of product which contains three hydroxy groups having similar solubility. These impurities can not be removed by repeated recrystallization of Sucralose even using different solvents. The present inventors have directed their research work towards developing a new process for purification of Sucralose which provides highly pure Sucralose without repeated recrystallization of substantially impure Sucralose.
Surprisingly, the present inventors have found that by converting substantially impure Sucralose to its penultimate intermediate i.e. TOPSA and then crystallizing it from an organic solvent significantly removes the impurities which were present in Sucralose. After purifying TOPSA, it can be converted to Sucralose by deacetylation. Unexpectedly the Sucralose obtained by this method is highly pure.